The presently disclosed embodiments relate generally to layers that are useful in imaging apparatus members and components, for use in electrostatographic, including digital, apparatuses. More particularly, the embodiments pertain to an electrostatographic imaging member having an improved charge blocking layer formed from an aqueous-based coating solution which exhibits improved shelf life and coating properties, such as increased homogeneity and adhesion, and methods for making the same.
In electrophotographic or electrostatographic printing, the charge retentive surface, typically known as a photoreceptor, is electrostatically charged, and then exposed to a light pattern of an original image to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on the photoreceptor form an electrostatic charge pattern, known as a latent image, conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder known as toner. Toner is held on the image areas by the electrostatic charge on the photoreceptor surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced or printed. The toner image may then be transferred to a substrate or support member (e.g., paper) directly or through the use of an intermediate transfer member, and the image affixed thereto to form a permanent record of the image to be reproduced or printed. The process is useful for light lens copying from an original or printing electronically generated or stored originals such as with a raster output scanner (ROS), where a charged surface may be imagewise discharged in a variety of ways.
The described electrostatographic copying process is well known and is commonly used for light lens copying of an original document. Analogous processes also exist in other electrostatographic printing applications such as, for example, digital laser printing or ionographic printing and reproduction where charge is deposited on a charge retentive surface in response to electronically generated or stored images.
Multilayered photoreceptors or imaging members have at least two layers, and may include a substrate, a conductive layer, an optional undercoat layer (sometimes referred to as a “charge blocking layer” or “hole blocking layer”), an optional adhesive layer, a photogenerating layer (sometimes referred to as a “charge generation layer,” “charge generating layer,” or “charge generator layer”), a charge transport layer, and an optional overcoat layer in either a flexible belt form or a rigid drum configuration. The undercoat layer is designed to block the charge injection from conductive substrate into CGL. The charge generation layer has the function generating free charges upon light exposure, and the function of charge transport layer is to transport the charges from CGL to the surface of photoreceptor. Enhancement of charge transport across these layers provides better photoreceptor performance. Multilayered flexible photoreceptor members may include an anti-curl layer on the backside of the substrate, opposite to the side of the electrically active layers, to render the desired photoreceptor flatness.
Current charge blocking layer in organic photoreceptor devices could be formed by one method of hydrolysis of organosilanes, such as for example, 3-aminopropyltriethoxysilane (γ-APS), using heptanes and ethanol as solvents in the coating process. However, the organic solvents in the process are associated with environmental risks and require high safety protection as well as lead to high manufacturing cost. Due to the limited miscibility between the components in the coating solution, the organic solvent involved coating process can easily have non-uniformity coating and coating defects, which cause poor photoreceptor performance and peel-off problems. As the charge blocking layer is applied on conductive substrate, such as titanium/zirconium metalized Mylar, the adhesion between the undercoat layer and the substrate is critical to maintain the entirety of the photoreceptor device. Thus, improved adhesion is necessary to ensure better photoreceptor performance and long application life.
Thus, there is a need for an improved imaging layer that does not suffer from the above-described problems.
Conventional photoreceptors are disclosed in the following patents, a number of which describe the presence of light scattering particles in the undercoat layers: Yu, U.S. Pat. No. 5,660,961; Yu, U.S. Pat. No. 5,215,839; and Katayama et al., U.S. Pat. No. 5,958,638. The term “photoreceptor” or “photoconductor” is generally used interchangeably with the terms “imaging member.” The term “electrostatographic” includes “electrophotographic” and “xerographic.” The terms “charge transport molecule” are generally used interchangeably with the terms “hole transport molecule or electron transport molecule.”